The semiconductor fabrication industry continues to source volatile metal containing precursors for vapor deposition processes, including chemical vapor deposition (CVD) and atomic layer deposition (ALD), plasma-enhanced ALD (PEALD) pulsed CVD, plasma enhanced CVD (PECVD) for fabricating conformal metal containing films on substrates, such as: silicon, metal, metal nitride, metal silicon nitride, metal oxide and other metal-containing layers, using these metal-containing precursors. The range of metals include those of the main group elements, transition metals, lanthanides and actinides. There is also a growing interest in volatile sources of chalcogenide based films containing such elements as germanium, antimony and tellurium for the growth of Phase Change Materials (PCM) for advanced memory applications. Additionally, any of these films can also be grown by super critical fluid deposition where the precursor is dissolved in a super critical fluid and a thin film grown from it.
For a metal compound to be useful as a volatile source for growing a metal containing film using the above mentioned processes it is typically important that it is stable enough to readily evaporate at elevated temperatures without decomposing, and similarly that its vapor is also thermally stable. This is acutely important for deposition processes such as ALD where the precursor vapor must be able to endure very high temperatures with no thermal decomposition occurring so that the film growth only occurs when the ALD reagent is cyclically added during the processing to build the growing film one layer at a time. If thermal decomposition of the precursor occurs then this effectively adds an undesired CVD component to the process and the step coverage of the growing film is degraded. In this respect, thermal stability of a precursor is highly prized. However, many precursors fall short of this ideal situation by decomposing at elevated temperatures. Currently, a major use of ALD in the semiconductor industry is the growth of metal oxides such as titanium oxide, zirconium oxide and lanthanide oxides. Often these processes are required to grow perfectly conformal films into deeply bored cylindrical volumes (vias) where it is imperative that there is no thermal decomposition or CVD component that will degrade conformality. One major mechanism by which precursors thermally degrade is when the anionic ligand to which the metal coordinates starts to decompose. Thus, making metal precursors which are coordinated to anions which are thermally robust is highly desirable.
Prior art in this field includes; WO 20099/086263 A1; US20090209777; US20090202740; US 2009/0200524; Journal of the American Chemical Society, 131, 4022-4026, 2009; M. Tadokoro, T. Shiomi, K. Lsob, K. Nakasuji, Inorganic Chem. 40 5476-5478 (2001); Inorg. Chem. 2008, 47, 2196-2204; applicant's own pending patent applications U.S. Ser. No. 12/785,041 priority May 29, 2009 and U.S. Ser. No. 61/301,824 filed Feb. 5, 2010.
The prior art has attempted to provide precursors for these applications. However, none of the metal complexes in the prior art share the special characteristic of the complexes disclosed in the present invention. The compounds disclosed herein are exceptional in their volatility and thermal stability under conditions of vaporization. This makes them highly effective as precursors for thin film growth and any other application which requires volatile sources of metal, metalloids or chalcogenides.